Comparison of fiber-optic linear beam shaping designs for laparoscopic laser sealing of vascular tissues

Infrared lasers may provide faster and more precise sealing of blood vessels and with lower device jaw temperatures than ultrasonic and electrosurgical devices during surgery. Our study explores three beam shaping methods using optical fibers for transformation of a circular laser beam into a linear beam, necessary for integration into a standard 5-mm-diameter laparoscopic device, and for uniform irradiation perpendicular to the vessel length. In the first design, a servo motor connected to a side-firing, 550-μm-core fiber, provided linear translation of a 2.0-mm-diameter circular beam, back, and forth, over either 5 or 11 mm scan lengths for sealing of small or large vessels. The second design used external beam splitters to divide laser power equally into three side-firing fibers, stacked side-by-side, producing a linear beam of 4 × 2 mm. The third design used external beam splitters with three forward-firing fibers and a slanted jaw surface, to produce a linear beam of 5 × 1.5 mm. Laser seals were performed, ex vivo, on 41 porcine renal arteries of 1- to 6-mm diameter (n ≥ 10 samples for each design). Each vessel was compressed to a fixed 0.4-mm-thickness, matching the optical penetration depth at 1470 nm. Vessels were irradiated with fluences of 636 to 800 J/cm², which, based on previous studies, is sufficient for sealing, but not cutting. A burst pressure setup was used to evaluate vessel seal strength. Reciprocating fiber and fiber bundles produced mean burst pressures of 554 ± 142, 524 ± 132, 429 ± 99, and 390 ± 140 mmHg, respectively. All designs consistently sealed blood vessels, with burst pressures above hypertensive (180 mmHg) blood pressures. The reciprocating fiber produced the most uniform linear beam profile and aspect ratio but will require integration of the servo motor into a handpiece. Fiber bundle designs produced shorter, less uniform beams, but enable optical components to be assembled outside the handpiece.

Optical Coherence Tomography Feedback System for Infrared Laser Sealing of Blood Vessels

Infrared (IR) lasers have recently been tested as an alternative to electrosurgical and ultrasonic laparoscopic devices for optical sealing of blood vessels. IR laser technology previously demonstrated faster sealing times, reduced thermal spread, and lower device temperatures during experimental studies. However, current commercial laparoscopic devices incorporate electrical impedance and/or temperature sensors as real-time, closed-loop, feedback to indicate successful blood vessel seals. This preliminary study explores an infrared laser system for sealing and optical coherence tomography (OCT) as a potential feedback system for successful vessel seal verification. A 1470-nm diode laser delivered an incident power of 30 W for an irradiation time of 5 s using an 8 × 2 mm linear beam, for creating strong seals in porcine renal blood vessels under compression. After sealing the blood vessels, OCT was performed on unsealed and sealed vessel regions for comparison. Standard vessel burst pressure (BP) measurements confirmed successful seals after OCT. Integrated reflectance intensity in OCT A-scans decreased by an average of 20 ± 6% in sealed versus native vessels of 2.4 ± 0.4 mm diameter. Vessel BP measured 532 ± 239 mmHg, with all vessels (n = 25) recording a successful BP > 180 mmHg (hypertensive blood pressure). Unsealed vessels demonstrated significantly deeper imaging marked by a continuous decay in reflected intensity, while sealed vessels showed subsurface reflectance intensity peaks, immediately followed by a rapid decay in reflectance intensity. These markers are consistent with increased light scattering and decreased optical penetration depth upon thermal coagulation of tissues. A-line OCT data consistently differentiated between sealed and unsealed blood vessel regions. Future work will involve OCT integration into the laparoscopic device for real-time optical feedback during IR laser sealing.

Reciprocating Side-Firing Fiber for Laser Sealing of Blood Vessels

Infrared lasers may provide faster and more precise sealing of blood vessels and with lower jaw temperatures than ultrasonic and electrosurgical devices. This study explores an oscillating or reciprocating side-firing optical fiber method for transformation of a circular laser beam into a linear beam, necessary for integration into a standard 5-mm-diameter laparoscopic device, and for uniform irradiation perpendicular to the vessel length. A servo motor connected to a side-firing, 550-μm-core fiber, provided linear translation of a 2.0-mm-diameter circular beam over either 5 mm or 11 mm scan lengths for sealing small or large vessels, respectively. Laser seals were performed, ex vivo, on a total of 20 porcine renal arteries of 1-6 mm diameter (n = 10 samples for each scan length). Each vessel was compressed to a fixed 0.4-mm-thickness, matching the 1470-nm laser optical penetration depth. Vessels were irradiated with fluences ranging from 636 J/cm² to 716 J/cm². A standard burst pressure (BP) setup was used to evaluate vessel seal strength. The reciprocating fiber produced mean BP of 554 ± 142 and 524 ± 132 mmHg, respectively, and consistently sealing blood vessels, with all BP above hypertensive (180 mmHg) blood pressures. The reciprocating fiber provides a relatively uniform linear beam profile and aspect ratio, but will require integration of servo motor into a handpiece.

Sealing and Bisection of Blood Vessels using a 1470 nm Laser: Optical, Thermal, and Tissue Damage Simulations

A 1470-nm laser previously demonstrated faster sealing and cutting of blood vessels with lower thermal spread than radiofrequency and ultrasonic surgical devices. This study simulates laser sealing and cutting of vessels in a sequential two-step process, for low (< 25 W), medium (~ 100 W), and high (200 W) power lasers. Optical transport, heat transfer, and tissue damage simulations were conducted. The blood vessel was assumed to be compressed to 400 μm thickness, matching previous experimental studies. A wide range of linear beam profiles (1-5 mm widths and 8-9.5 mm lengths), incident powers (20-200 W) and irradiation times (0.5-5.0 s), were simulated. Peak seal and cut temperatures and bifurcated thermal seal zones were also simulated and compared with experimental results for model validation. Optimal low power laser parameters were: 24W/5s/8×2mm for sealing and 24W/5s/8×1mm for cutting, yielding thermal spread of 0.4 mm and corresponding to experimental vessel burst pressures (BP) of ~450 mmHg. Optimal medium-power laser parameters were: 90 W/1s/9.5×3mm for sealing and 90W/1s/9.5×1mm for cutting, yielding thermal spread of 0.9 mm for BP of ~1300 mmHg. Optimal high-power laser parameters were: 200W/0.5s/9×3mm for sealing and 200W/0.5s/9×1mm for cutting, yielding thermal spread of 0.9 mm and extrapolated to have BP of ~1300 mmHg. All lasers produced seal zones between 0.4-1.5 mm, correlating to high BP of 300-1300 mmHg. Higher laser powers enable shorter sealing and cutting times and higher vessel seal strengths.